2013-06-10

Monday Roundup: Light Emitting Integrated Circuits

This week: saving the turtles, a 173 lumen/Watt tube, and a step towards the next level of LED integration.

Cross-section of RPI's monolithically integrated GaN LED and HEMT (Source: Chow et al.)

Monolithic integration of LED and HEMT on GaN chip
At Rensselaer Polytechnic Institute, researchers have etched a high-power transistor into GaN (specifically, a high-electron-mobility transistor, or HEMT), built up a GaN LED in layers beside it, and interconnected the two.

The press release does not say so directly, but the intermediate aim seems to be to create the components of a power supply and driver out of the same GaN that constitutes the LED. In the long run the goal may be more ambitious: to produce out of the same material the logic gates and radios capable of running a ZigBee stack and perhaps Bluetooth.

The study appeared in Applied Physics Letters last month and was titled "Monolithic integration of light-emitting diodes and power metal-oxide semiconductor channel high-electron-mobility transistors for light-emitting power integrated circuits in GaN on sapphire substrate." The team was led by T. Paul Chow, professor in the Department of Electrical, Computer, and Systems Engineering at RPI.

The researchers "demonstrated light output and light density comparable to standard GaN LED devices," according to the press release, and "Chow reckons that the study is a key step toward creating a new class of optoelectronic device: the light-emitting integrated circuit (LEIC)."

Coastal Light (Image: LSGC)

Saving the turtles
Lighting Science Group has introduced a Coastal Light, which is designed to be friendly to non-human living things near the seashore. In particular the company is stressing the friendliness of the amber-colored light to hatchling sea turtles, which have been getting disoriented by bright lights near the shore and failing to make it into the ocean, as their survival requires. Every year, some 20,000 of the endangered creatures have been perishing after being disoriented by bright, white lights near the shore. Sea turtles' vision has a peak sensitivity higher up the spectrum than humans' does, extending into the ultraviolet, and amber or red light does not cause them any problems.

Efficacy watch: 173 lm/W
Green Ray LED Lighting has developed an 8-foot LED light, in the form of a fluorescent replacement tube, which it claims achieves a luminous efficacy of 173 lumens per Watt. The tube is somewhere between R&D and a released product at this point, and the Green Ray website does not indicate when it might ship. The company says that its tube has undergone US Department of Energy testing and has qualified for the "Lighting Facts" label, which means that DoE validates the efficacy number.

Philips Lighting made a splash in April with its announcement of a 200 lm/W, warm-white fluorescent replacement tube, due to hit the market in 2015.

LEDs for cows
A while back we had a look at LEDs being put to work lighting turkey barns. Now let's turn our attention to bovines.

DairyHerd.com profiles one farmer in Iowa who replaced 70 8-foot T-2 and T-12 fluorescent tubes with LED equivalents. The source was Zeus LED Inc. from Carbondale, Iowa, which designs lamps for manufacture in China. The farmer reports saving 60 percent on his electricity bill. He expects the energy savings to repay the investment in 3.8 years, after factoring in government rebates -- it would have been 5.6 years without. The LEDs generate 104 to 110 lumens per Watt, vs. 70 or 80 for the fluorescents they replaced.

It is possible that LED lighting increases cows' production of milk. That's the conclusion of a small-scale study published last year out of Oklahoma State University. The researchers who carried out the "split-barn" study aren't sure what caused the increase -- an effect related to hormones, the cows eating more in the brighter conditions, or something else.

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— Keith Dawson , Editor-in-Chief, All LED Lighting